Conventionally, semiconductor power devices have occupied a large area to control a large current and achieve a low loss. For example, discrete power devices each with many vertical MISFETs integrated on a whole Si wafer with a size of 4 or more inches are commercially available. Each of the vertical MISFETs is a semiconductor element. For example, see the following document: “Power Device/Power IC Handbook”, edited by the Research Committee of High-Performance, Sophisticated Power Device/Power IC, the Institute of Electrical Engineers of Japan, published by Corona Publishing Co., Ltd., Jul. 30, 1996, page 4. The reason why one power device is constructed by integrating many vertical MISFETs is that the current flow area of the MISFET is distributed to avoid the localization of a heat-producing part.
On the other hand, wide band-gap semiconductor devices constructed by using a wide band-gap semiconductor such as silicon carbide (SiC), Group-III nitride such as GaN and AlN, or diamond are researched and developed for practical use, because they are expected to provide a high-speed operation, a high breakdown voltage and a low loss in terms of material properties.
Silicon carbide indicated as “SiC” is a material that is distinct in physical and chemical properties from silicon that is indicated as “Si:C” and contains a very small quantity (a few % or less) of C.